EPA'S DIOXIN REASSESSMENT--PART 2:
DIOXIN DAMAGES HUMAN IMMUNE SYSTEM

U.S. Environmental Protection Agency [EPA] is presently
reassessing the dangers of dioxin, one of the most toxic
chemicals ever tested on laboratory animals. As a result of
animal tests, EPA has declared only exceedingly small amounts of
dioxin "safe" for the human food supply. Americans eat food
routinely containing roughly 10 to 100 times more dioxin than EPA
considers safe. [SEE RHWN #269.]

No one makes dioxin intentionally, but many industries create
dioxin as a byproduct of their main activity. Industries that
emit dioxin into the environment (paper, plastics, chemicals, and
solid waste incinerators) are being sued for their emissions by
citizens claiming harm from exposure, and one
industry--paper--faces billions of dollars in lawsuits.

Partly to please the paper industry, and partly because there
were new scientific findings worth considering, EPA chief William
Reilly announced a year-long dioxin reassessment to begin in
April, 1991.

Now, nine months into the year-long process, EPA scientists
responsible for parts of the reassessment have begun talking
openly about new findings that make dioxin seem as bad as, or
worse than, EPA used to think.

For two decades dioxin has baffled toxicologists. They are used
to seeing cancer-causing chemicals that predominantly cause
cancer in one organ or another--like asbestos, which chiefly
affects the lungs, or benzene, which chiefly affects the
blood-forming cells, causing leukemia. But dioxin seems to cause
cancer in many organs, raising the general level of cancer in a
population without causing a huge increase in any one type of
cancer. In addition, dioxin causes certain toxic effects in one
species and other effects in another species. Likewise, dioxin at
low doses causes one kind of illness, and at higher doses it
causes different illnesses. Only recently have EPA scientists
concluded that this puzzling pattern occurs because dioxin acts
like an "environmental hormone." Hormones are potent natural
chemicals that send messages via the bloodstream, turning on and
off chemical switches throughout the body, creating an array of
effects in different organs. Dioxin behaves this way. Hormones
are present in the body in tiny amounts, yet they can trigger
huge changes in various bodily systems. For example, it is
hormones that trigger the different stages of growth in a fetus,
and that cause young humans to go through puberty.

New Information

EPA chief William Reilly was right--there IS new information
about dioxin. But it won't be reassuring to the paper industry.
On the contrary, two studies of workers exposed to dioxin,
published during the past year, have shown unmistakable increases
in cancers of several types. A study of 5172 American workers
revealed a cancer rate 46% above the norm.[1] Likewise, a study
of 1583 German workers revealed a cancer rate 39% above the norm;
among German workers 20 years on the job, the rate was 82% above
the norm, and among the most heavily exposed Germans workers, the
cancer rate was three times the norm.[2] Notably, among female
German workers, the risk of breast cancer was doubled. Whereas a
year ago one might have argued whether dioxin had ever been shown
to cause cancer in humans, now such arguments are only voiced by
the kind of people who say it still isn't proven that cigarettes
cause lung cancer.

Linda Birnbaum, one of the scientists conducting EPA's
reassessment of dioxin, says these two studies have convinced her
that dioxin causes cancer in humans, at least at relatively high
exposures. But, she told SCIENCE NEWS (January 11, 1992, pgs.
24-27.), she has an even greater concern about dioxin: "I'm very
concerned that much lower exposure to dioxin may result in
adverse health effects that are very subtle and difficult to
detect." She was talking about dioxin's impact on the immune
system.

The immune system is an exceedingly complex network of organs,
cells, and chemical secretions (hormones) that react to preserve
health in the face of a vast array of hostile microorganisms and
toxicants that our bodies encounter every day. The immune system
fights against common colds, influenza, and the body's own cells
that go haywire and start to multiply uncontrollably (a
definition of cancer).

A degraded immune system leaves the body less able to defend
itself against hostile forces in the natural environment. Dioxin
attacks the immune system.

EPA's dioxin reassessment will "focus much greater attention on
toxicological data revealing TCDD's [dioxin's] reproductive,
developmental, and immunotoxic effects," says SCIENCE NEWS.
Immunotoxic means toxic to the immune system. Furthermore, "This
document [EPA's draft reassessment][ will also establish TCDD as
the first pollutant to be regulated on the basis of toxicity
observed at the cellular level."

This is one reason why the dioxin controversy is being followed
so carefully by industry and by environmentalists. It promises to
set precedents in the way chemicals are regulated in the future.
In the past, chemicals were considered harmless if they caused no
"clinical" damage (damage your family doctor might detect). Now,
with the dioxin reassessment, evidence of chemical changes inside
individual cells is being considered important to a person's well
being.

"So far, studies in mice suggest that dioxin's immunotoxic punch
occurs in extremely low doses and may well be more important than
cancer in determining dioxin's primary health risk," says
Birnbaum."

To study TCDD's toxicity to the immune system, researchers use
mice, whose immune systems model those of humans. For example,
EPA researchers have measured how well TCDD-treated mice
withstand the influenza virus. Mice pre-treated with TCDD readily
die after exposure to a quantity of virus that rarely kills
healthy mice.

Naturally, it would be very difficult to detect such effects in
people. If people exposed to unusually high levels of dioxin, say
from a solid waste incinerator, had damaged immune systems and
consequently experienced various illnesses, no one might ever
suspect dioxin as a cause.

People might question whether some of dioxin's low-level effects
represent real harm to people, but "...few people will contend
that suppression of the immune system is not an adverse health
effect," Birnbaum told SCIENCE NEWS.

Unlike hormones, which remain in the body only a few hours,
dioxin has a half-life in the body of seven years. At the end of
one half-life, half the initial dioxin remains. What this means
is that dioxin has, relatively, a very long half-life in the
body, unlike the hormones that it mimics, so it stays around to
play havoc with the body's chemical systems year after year.
"Thus one TCDD [dioxin] molecule can continuously disrupt normal
cell physiology," says SCIENCE NEWS, citing work by well-known
dioxin researcher Thomas A. Gasiewicz at the University of
Rochester (NY) Medical School. EPA's Birnbaum, and Michael
Holsapple, a well-known di-oxin researcher at the Medical College
of Virginia, say studies of humans at Times Beach, Missouri, and
of Vietnam veterans, were essentially bungled. Holsapple says,
"If I were to take mice and ask the same [research] questions
that are routinely asked of the populations of Times Beach or in
the Ranch Hand study [of Vietnam vets exposed to
dioxin-contaminated herbicide], I would come up with a very
nebulous picture [of dioxin's immunotoxicity]," says Holsapple.
"But when we ask different questions [in mice], we can certainly
show very strong effects on the immune response," he says.

Is there a threshold for dioxin's damage to the human body? Is
there a level of dioxin below which no effects can be observed?
George Lucier of the National Institute of Environmental Health
Sciences in Research Triangle, North Carolina, has been asking
this question in his laboratory. His data show no evidence of any
threshold. "My data might not prove that a threshold doesn't
exist," he told SCIENCE NEWS, "but there's also no evidence of
any thresholds." In other words, any amount of dioxin does some
damage, according to Lucier's findings. This means the only safe
amount is zero.

This conclusion is not what the paper industry wanted to hear
when its executives urged William Reilly to initiate EPA's dioxin
reassessment. As the reassessment reaches its draft stages early
this summer, we'll have new measures of the potency not only of
dioxin, but also of industry's muscle in a contest with unwelcome
scientific conclusions.